Craft beers and crafty bugs

Wandering among the Elephant Rocks on the Vanished World Trail around Duntroon. Little did they suspect what awaited them at home…. Image by Adrian Paterson.

I have to admit a certain fondness for craft beers. I particularly like the big tasting American pale ales but will generally try any old thing that I come across. There is certainly a large diversity of craft beers around and it taps into that collector gene that gets you excited when you see a new company or variety. As such I usually have a fair few bottles of craft beer in the pantry. And then came the night of the teenage party.

Julie and I happened to be away one recent weekend, enjoying the vanished world of Duntroon and the seafood of Fleur’s Place at Moeraki. Youngest son was left on his own at home. Youngest son decided to get a few mates around to watch the All Blacks rugby test. One thing lead to another and before he realized it we had 70 ‘guests’, most that he didn’t know. Despite youngest son and his friends getting rid of the unwanted a couple of hours later, we returned the next day to find sodden carpets, some broken windows, missing bits and pieces, and a sheepish son.

What about the craft beers? I hear your concern. Initially I thought they were all gone. But on closer examination at least half of them survived and about half of those that were opened were left half drunk. Given the sheer number of empty cans and bottles that we put out to recycle it seems odd that any beer in the house would survive a teenage plague. Which brings me to mites and Hemipteran bugs.

A predatory mite (Anystis baccarum) attacks a nymph of the tomato potato psyllid (Bactericera cockerelli). Image by Ian Geary.

The tomato potato psyllid is an important pest of, well, tomatoes and potatoes in the Americas and now New Zealand. These psyllids suck sap from the plants, damaging them and spreading a bacterial disease. Control of these psyllids is largely through insecticides but we are constantly looking for different methods, particularly those with a biological control bent. One of the predators of tomato potato psyllids is the predatory mite Anystis baccarum. These mites have been observed on crops of organic potatoes eating psyllid nymphs. What we need to know is whether the mites could eat enough psyllids to control their numbers in more general situations.

Honours student Ian Geary, working with several Lincoln University staff, decided to get more detail on how these mites interact with the psyllids. They have published their study in the New Zealand Entomologist. Ian prepared ‘leaf arenas’ into which a late instar psyllid nymph was placed. Tomato Potato psyllids, like other bug species, excrete sugar droplets. The psyllids were allowed to forage and produce several sugar droplets (which were left or removed depending on the experiment). Some of the psyllids were then flipped onto their backs while other were left right-way-up. Then mites were transferred into the arena.

Mites searched the leaf arena and on contact with a psyllid would start to probe the underside of the psyllid as a prelude to an attack. Those psyllids that were right way up would pull their carapace down against the leaf and the mites were often unable to make much progress. Those psyllids that were upside down were much more vulnerable and were frequently successfully attacked by the mites.

But the tomato potato psyllids had another trick to play in this conflict. The sugar that is excreted by the psyllid plays an important role in defense. When mites explored the arena they would often come into contact with the sugar. The mites would then spend time investigating and consuming the sugar. In the long term this resulted in only about 10% of psyllids being consumed in arenas with sugar compared to 40-50% where sugars were not present.

A predatory mite investigates sugar crystals excreted by the tomato potato psyllid. Image by Ian Geary.

So Anystis mites might not be a great biocontrol agent for tomato potato psyllids as they appear easily distracted by tempting sugar treats. And this may provide a clue for how my craft beers survived the teen plague. Most common draft beers, ciders and alcopops are very sweet. Craft beers usually dial down the sugar and increase the bitter and hoppy flavours. So teens, preferring sweetness, focus on the more mainstream drinks. The craft beers that were opened only had a few mouth-fills out of them, enough to register the lack of sweetness and warn the rest of the horde!

So some free advice to parents of teens, act like the psyllids and keep sugary ‘decoy drinks’ around your craft beers and nice wines and they may survive impromptu teen parties!

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